Flexible optical multiplexer

ABSTRACT

A multiplexer has an optical circulator including at least first, second and third circulator ports. An optical fiber with a first optical transmission path is coupled to the first circulator port of the optical circulator. The optical fiber carries a wavelength division multiplexed optical signal, including signals λ 1 -λ n , and at least one signal λ 1  to be dropped by the multiplexer. A second optical transmission path is in optical communication with the second circulator port. A first filter is coupled to the second optical transmission path. The first filter passes a portion of the λ 1  signal, and reflects a first residual λ 1  signal and signals λ 2 -λ n  to the optical circulator. A third optical transmission path is in optical communication with the third circulator port and transmits the signals λ 2 -λ n  received from the optical circulator.

CROSS-REFERENCE TO RELATED APPLICATION

The present invention is a continuation-in-part of provisionalapplication Ser. No. 60/121,456, filed Feb. 24, 1999, pending, which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to optical multiplexers, and moreparticularly to wavelength selectable optical multiplexers andde-multiplexers.

2. Description of Related Art

Optical communication systems are a substantial and fast-growingconstituent of communication networks. As used herein, an opticalcommunication system, relates to any system which uses optical signalsto convey information across an optical waveguiding medium. Such opticalsystems include, but are not limited to, telecommunications systems,cable television systems, and local area networks (LANs). Opticalsystems are described in Gowar, Ed. Optical Communication Systems,(Prentice Hall, N.Y.) c. 1993, the disclosure of which is incorporatedherein by reference. Currently, the majority of optical communicationsystems are configured to carry an optical channel of a singlewavelength over one or more optical waveguides. To convey informationfrom plural sources, time-division multiplexing is frequently employed(TDM). In time-division multiplexing, a particular time slot is assignedto each information source, the complete signal being constructed fromthe signal portion collected from each time slot. While this is a usefultechnique for carrying plural information sources on a single channel,its capacity is limited by fiber dispersion and the need to generatehigh peak power pulses.

While the need for communication services increases, the currentcapacity of existing waveguiding media is limited. Although capacity maybe expanded, e.g., by laying more fiber optic cables, the cost of suchexpansion is prohibitive. Consequently, there exists a need for acost-effective way to increase the capacity of existing opticalwaveguides.

Wavelength division multiplexing (WDM) has been explored as an approachfor increasing the capacity of existing fiber optic networks. A WDMsystem employs plural optical signal channels, each channel beingassigned a particular channel wavelength. In a WDM system, opticalsignal channels are generated, multiplexed to form an optical signalcomprised of the individual optical signal channels, transmitted over asingle waveguide, and de-multiplexed such that each channel wavelengthis individually routed to a designated receiver. Through the use ofoptical amplifiers, such as doped fiber amplifiers, plural opticalchannels are directly amplified simultaneously, facilitating the use ofWDM systems in long-distance optical systems. Exemplary WDM opticalcommunication systems are described in commonly-assigned U.S. Pat. Nos.5,504,609, 5,532,864, and 5,557,442, the disclosures of which areincorporated herein by reference.

In many applications, such as optical LANs, cable television subscribersystems, and telecommunications networks, there is a need to route oneor more channels of a multiplexed optical signal to differentdestinations. Such routing occurs when optical channels are sent to orwithdrawn from an optical transmission line e.g., for sending opticalchannels between a terminal and an optical bus or routing long distancetelecommunications traffic to individual cities. This form of opticalrouting is generally referred to as optical add-drop multiplexing.

The most prevalent device used for combining and extracting wavelengthsin a DWDM system is an Array Waveguide (AWG). The AWG suffers from anundesirable side effect that requires each port transmit, or receive inthe case of a de-multiplexer, only one specific, pre-determinedwavelength and sequential wavelengths. This is problematic in the casethat one of the transmitters fails. A new transmitter of the identicalwavelength must be added to that specific port. A second multiplexerdesign uses couplers that have the unpleasant side effect of adding−10logN to 3log₂NdB of loss at each stage of coupling.

There is a need for a DWDM device, sub-system and system withflexibility in design, configuration and degree of system refinement.There is another need for multiplexing that frees transmitters to useany port. A further need exists for flexible construction ofmultiplexers and de-multiplexers using different circulator port countsand interchangeable device types. There is a further need for the use ofvariable tunable filters working in concert to tailor a DWDM signal forgain flatness as well as other applications. Another need exists forDWDM devices, sub-systems and systems with low cross-talk.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a DWDM device,sub-system or system that provides improved flexibility in design,configuration and system refinement.

Another object of the present invention is to provide a DWDM device,sub-system or system that is tunable.

Yet another object of the present invention is to provide a DWDM device,sub-system or system that is programmably tunable.

A further object of the present invention is to provide a DWDM device,sub-system or system that is flexible and provides for differentconfiguration, different levels of filtration as well as differentcombinations of wavelengths that are multiplexed and de-multiplexed.

Still another object of the present invention is to provide a tunableDWDM device with one or more filters to reduce crosstalk.

Another object of the present invention is to provide a positionindependent method and device for combining or separing many wavelengthsinto or from a single optical fiber.

Yet another object of the invention is to provide a wavelength tunablevariable optical tap.

Another object of the invention is to provide a drop and continuenetwork node.

These and other objects of the invention are provided in a multiplexerwith an optical circulator including at least first, second and thirdcirculator ports. An optical fiber with a first optical transmissionpath is coupled to the first circulator port of the optical circulator.The optical fiber carries a wavelength division multiplexed opticalsignal, including signals λ₁-λ_(n), and at least one signal λ₁ to bedropped by the multiplexer. A second optical transmission path is inoptical communication with the second circulator port. A first filter iscoupled to the second optical transmission path. The first filter passesa portion of the λ₁ signal, and reflects a first residual λ₁ signal andsignals λ₂-λ_(n) to the optical circulator. A third optical transmissionpath is in optical communication with the third circulator port andtransmits the signals λ₂-λ_(n) received from the optical circulator.

In another embodiment, a multiplexer for a wavelength divisionmultiplexed optical communication system has an optical circulator withat least first, second, third and fourth circulator ports. An opticalfiber with a first optical transmission path is coupled to the firstcirculator port and carries a wavelength division multiplexed opticalsignal including signals λ₁-λ_(n). A second optical transmission path isin optical communication with the second circulator port. A firstdetector/filter is coupled to the second optical transmission path. Thefirst detector/filter detects a λ₁ signal, passes a portion of the λ₁signal, and reflects a first residual λ₁ signal and the signals λ₂-λ_(n)to the optical circulator. A third optical transmission path is inoptical communication with the third circulator port and transmits thesignals λ₁-λ_(n) received from the optical circulator. A fourth opticaltransmission path is in optical communication with the fourth opticalcirculator port. The fourth optical transmission path is positionedafter the second optical transmission path and before the third opticaltransmission path. A first optoelectronic device is coupled to thefourth optical transmission path.

In another embodiment, a first filter is substituted for the firstdetector/filter. The first filter does not detect the λ₁ signal. Thefirst filter passes a portion of the λ₁ signal, and reflecting the firstresidual λ₁ signal and the signals λ₂-λ_(n) to the optical circulator.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of an embodiment of the present inventionillustrating a DWDM system.

FIG. 2 is a schematic diagram of multiplexer or de-multiplexer of thepresent invention that includes a three port optical circulator and afilter that is reflective and transmissive coupled to the opticalcirculator.

FIG. 3 is a schematic diagram of multiplexer or de-multiplexer thatincludes a four port optical circulator and a detector/filter thatdetects and passes a portion of a signal, reflects a residual portion ofthe passed signal along with all other signals, as well as a secondoptoelectronic device coupled to the optical circulator.

FIG. 4 is a schematic diagram of the multiplexer or de-multiplexer ofFIG. 3 with an additional optical circulator port, optical transmissionpath and a third optoelectronic device.

FIG. 5 is a schematic diagram of the multiplexer or de-multiplexer ofFIG. 4 with an additional optical circulator port, optical transmissionpath and a fourth optoelectronic device.

FIG. 6 is a schematic diagram of multiplexer or de-multiplexer thatincludes a four port optical circulator and a filter that passes aportion of a signal, reflects a residual portion of the passed signalalong with all other signals, as well as a second optoelectronic devicecoupled to the optical circulator.

FIG. 7 is a schematic diagram of the multiplexer or de-multiplexer ofFIG. 6 with an additional optical circulator port, optical transmissionpath and a third optoelectronic device.

FIG. 8 is a schematic diagram of a multiplexer or de-multiplexer of thepresent invention that includes a four port optical circulator, a lasercoupled to the second port and an optoelectronic device coupled to thefourth port.

FIG. 9 is a schematic diagram of the multiplexer or de-multiplexer ofFIG. 8 with a second optoelectronic device coupled to an additionaloptical circulator port.

FIG. 10 is a schematic diagram of a multiplexer or de-multiplexer of thepresent invention with two optical circulators and an optoelectronicdevice coupled to each optical circulator.

FIG. 11 is a schematic diagram of the multiplexer or de-multiplexer ofFIG. 10 that includes a residual filter positioned between the first andsecond optical circulators.

FIG. 12 is a schematic diagram of a multiplex or de-multiplexer of thepresent invention with an input fiber, a substrate, a firstoptoelectronic device positioned on a surface of the substrate and asecond optoelectronic device.

FIG. 13 is a schematic diagram of a multiplex or de-multiplexer of thepresent invention with an input fiber, a first substrate, a secondsubstrate that faces the first substrate, a first optoelectronic devicepositioned on a surface of the first substrate, a second optoelectronicdevice positioned at a surface of the second substrate and a thirdoptoelectronic device.

FIG. 14 is a schematic diagram of a multiplex or de-multiplexer of thepresent invention with an input fiber, a first substrate with a firstsubstrate surface, a second substrate with a reflective surface thatfaces the first substrate, first and second optoelectronic devicespositioned at the surface of the first substrate, and a thirdoptoelectronic device.

FIG. 15 is a schematic diagram of a multiplexer of the present inventionthat includes a three port optical circulator, and first and secondlasers coupled to the first and second ports.

FIG. 16 is a schematic diagram of a de-multiplexer of the presentinvention that includes a three port optical circulator, with first andsecond detector/filters and/or filters coupled to the second and thirdports.

DETAILED DESCRIPTION

The present invention provides DWDM systems, sub-systems and devices.The present invention is applicable to coarse or widewavelength-division multiplexing. Sub-systems of the present inventioninclude but are not limited to multiplexers, de-multiplexers, add/dropmultiplexers, gain flatteners, taps and filters. In one embodimentillustrated in FIG. 1, a DWDM system 10 includes a multiplexer, ade-multiplexer and a DWDM sub-system that is coupled to the multiplexerand the de-multiplexer. Also included are one or more amplifiers. TheDWDM systems, sub-systems and devices of the present invention provideimproved flexibility of wavelength adding, combining, dropping,separating and leveling. The DWDM devices, sub-systems and systems ofthe present invention permit different system and sub-system, (i)configurations, (ii) levels of signal filtration and (ii) combinationsof signals that are multiplexed and de-multiplexed.

In one embodiment of the present invention, the DWDM systems,sub-systems and devices have low cross talk that is better than 20 dB.It will be appreciated that the present invention is not limited tocross talk that is better than 20 dB.

Referring now to FIG. 2, one embodiment of the invention is amultiplexer 10 that includes an optical circulator 12 with at leastfirst, second and third circulator ports 14, 16 and 18 respectively.Multiplexer 10 can includes any number of circulator ports. An opticalfiber with a first optical transmission path 20 is coupled to firstcirculator port 14. The optical fiber carries a wavelength divisionmultiplexed optical signal, including signals λ₁-λ_(n), and at least onesignal λ₁ to be dropped by multiplexer 10. The signal λ₁ can be any ofthe signals λ₁-λ_(n). A second optical transmission path 22 is inoptical communication with second circulator port 16. A first filter 24is coupled to second optical transmission path 22. Filter 24 istransmissive in one or more signals and reflective of all other signals,has a high degree of reflectivity, works well across the entire DWDMspectrum and has minimal gain slope. Filter 24 passes a portion of theλ₁ signal, and reflects a first residual λ₁ signal and signals λ₂-λ_(n)to optical circulator 12. A third optical transmission path 26 is inoptical communication with third circulator port 18 and transmits thesignals λ₂-λ_(n) received from the optical circulator. Filter 24 reducesthe cross-talk of multiplexer 10. In one embodiment, one detector and atleast two filters 24 bring down the cross talk to 50 dB, and morepreferably 45 dB.

Another embodiment of a multiplexer 10 of the present invention isillustrated in FIG. 3. Optical circulator has four optical circulatorports 14, 16, 18 and 30. A detector/filter 28 is coupled to secondoptical transmission path 22. Detector/filter combines the two functionsof detection and filtering and is typically an integrated device.Detector/filter 28 detects the λ₁ signal, passing a portion of the λ₁signal, and reflects a first residual λ₁ signal and signals λ₂-λ_(n) tooptical circulator 12. Preferably, a majority of the signal λ₁ ispassed. Preferably, at least 95% of the signal λ₁ is passed, and morepreferably 99%. Detector/filter 28 can be an integral or a non-integraldetector and filter device. Fourth optical transmission path 32 ispositioned between second and third optical transmission paths 22 and26. An optoelectronic device 34 is coupled to fourth opticaltransmission path 32. In this embodiment, multiplexer 10 is an opticaltap, add-drop multiplexer or gain/loss equalization device.

Optoelectronic device 34 can be a detector/filter, a filter or a laser.Suitable lasers and laser assemblies are disclosed in U.S. PatentApplications, Attorney Docket Nos. 21123-701, 21123-702, 21123-703,filed on the same date of this application and incorporated herein byreference. When optoelectronic device 34 is a detector/filter or afilter, multiplexer 12 is an optical drop or gain equalization device.When optoelectronic device 34 is a laser, multiplexer 12 is an add-dropmultiplexer. Detector/filter 34 detects the first residual λ₁ signal,passes the first residual λ₁ signal and reflects a second residual λ₁signal and the signals λ₂-λ_(n) which are received at optical circulator12. The second residual λ₁ signal has a few percent, preferably 5% orless, of the original first residual λ₁ signal, and more preferably only0.1%. Filter 34 does not detect the signal λ₁. Filter 34 passes thefirst residual λ₁ signal and reflects the second residual λ₁ signal andthe signals λ₂-λ_(n) which are again received at optical circulator 12.Laser 34 reflects the first residual λ₁ signal and the signals λ₂-λ_(n)and adds back the signal λ₁. Laser 34 preferably is a laser emitting anITU grid wavelength with a front face with high reflectivity (up to 99%)to incident wavelengths other than the lasing wavelength. Instead ofadding back the signal λ₁ laser 34 can add a new signal, the λ_(n+1)signal.

Referring now to FIG. 4, multiplexer 10 can further include a fifthoptical transmission path 36 in optical communication with a thirdoptical circulator port 38. Fifth optical transmission path 36 ispositioned between fourth and fifth optical transmission paths 32 and 26respectively. A second optoelectronic device 40 is coupled to fifthoptical transmission path 36. Second optoelectronic device 40 can be adetector/filter, filter or laser. In the embodiment of FIG. 4,detector/filter 28 is coupled to second optical transmission path 22.One of detector/filter 34, filter 34 or laser 34 is coupled to fourthoptical transmission path 32.

In FIG. 4, when detector/filter 34 is coupled to fourth opticaltransmission path 32, detector/filter 40 detects the second residual λ₁signal, passes the second residual λ₁ signal and reflects a thirdresidual λ₁ signal and the signals λ₂-λ_(n) which are received atoptical circulator 12. Filter 40 passes the second residual λ₁ signaland reflects the third residual λ₁ signal and the signals λ₂-λ_(n) whichare again received at optical circulator 12. In this embodiment,multiplexer 12 is an optical drop, add-drop multiplexer or gain/lossequalization device. Laser 40 reflects the second residual λ₁ signal andthe signals λ₂-λ_(n), and either adds back the signal λ₁ or adds a newλ_(n+1) signal. In this embodiment, multiplexer 12 is an add-dropmultiplexer.

Further in FIG. 4, when laser 34 is coupled to fourth opticaltransmission path, detector/filter 40 detects the first residual λ₁signal, passes the first residual λ₁ signal and reflects a secondresidual λ₁ signal, the signals λ₂-λ_(n) and the signal λ_(n+1). Filter40 passes the first residual λ₁ signal and reflects a second residual λ₁signal, the signals λ₂-λ_(n) and the signal λ_(n+1). Laser 40 reflectsthe first residual λ₁ signal, the signals λ₂-λ_(n), the signal λ_(n+1)and adds back the signal λ₁ or adds a new signal λ_(n+2).

As shown in FIG. 5, a sixth optical transmission path 42 is in opticalcommunication with a sixth optical circulator port 44. Sixth opticaltransmission path 42 is positioned after between fifth and third opticaltransmission paths 36 and 26. An optoelectronic device 46 is coupled tosixth optical transmission path 42. Optoelectronic device 46 can be adetector/filter, filter or laser.

In FIG. 5, when detector/filter 34 or filter 34 is coupled to fourthoptical transmission path 32, and detector/filter 40 or filter 40 iscoupled to fifth optical transmission path 36, laser 46 reflects thethird residual λ₁ signal, the signals λ₂-λ_(n) and adds back the signalλ₁ or adds the new signal λ_(n+1).

In each of FIGS. 2-5, a bidirectional optical amplifier 48 can becoupled to any of the second, third, fourth, fifth or sixth opticaltransmission paths 22, 32, 36 and 42 respectively, and positionedbetween the optoelectronic device and optical circulator 12.Bi-directional optical amplifier 48 has low noise, flat gain and is ableto handle the entire DWDM signal range. Additionally, some or all ofdetector/filter, filter, bidirectional amplifier and laser 28, 34, 40and 48 can be programmably or non-programmably tunable.

In the embodiment illustrated in FIG. 6, filter 24 is coupled to secondoptical transmission path 22. Filter 24 passes a majority of the signalλ₁ and reflects the first residual λ₁ signal and signals λ₂-λ_(n) tooptical circulator 12. An optoelectronic device 34 is coupled to fourthoptical transmission path 30. Optoelectronic device 34 can be a filter,detector/filter, laser amplifier or attenuator.

When optoelectronic device 34 is a filter, multiplexer 10 is an opticaltap, optical drop or gain/loss equalization device. Filter 34 passes thefirst residual λ₁ signal and reflects the second residual λ₁ signal andthe signals λ₂-λ_(n) which are again received at optical circulator 12.When optoelectronic device 34 is a detector/filter, multiplexer 12 is anoptical drop or gain equalization device. Detector/filter 34 detects thefirst residual λ₁ signal, passes the first residual λ₁ signal andreflects a second residual λ₁ signal and the signals λ₂-λ_(n) which arereceived at optical circulator 12. When optoelectronic device 34 is alaser, multiplexer 12 is an add-drop multiplexer. Laser 34 adds back thesignal λ₁ or adds a new signal, the λ_(n+1) signal.

Referring now to FIG. 7, multiplexer 10 of FIG. 6 can further includesecond optoelectronic device 40 coupled to fifth optical transmissionpath 36. Second optoelectronic device 40 can be a detector/filter,filter, laser amplifier or attenuator. Multiplexer 12 is an optical tap,optical drop, add-drop multiplexer or gain equalization device whensecond optoelectronic device is filter 40; an optical drop, gainequalization device, add-drop multiplexer or optical tap when secondoptoelectronic device is detector/filter 40; and an add-drop multiplexerwhen second optoelectronic device 40 is laser 40.

In FIG. 7, when detector/filter 34 or filter 34 are coupled to fourthoptical transmission path 32, detector/filter 40 detects the secondresidual λ₁ signal, passes the second residual λ₁ signal and reflects athird residual λ₁ signal and the signals λ₂-λ_(n) which are received atoptical circulator 12. Filter 40 passes the second residual λ₁ signaland reflects the third residual λ₁ signal and the signals λ₂-λ_(n) whichare again received at optical circulator 12. Laser 40 reflects thesecond residual λ₁ signal and the signals λ₂-λ_(n), and either adds backthe signal λ₁ or adds a new λ_(n+1) signal.

Further in FIG. 7, when laser 34 is coupled to fourth opticaltransmission path, detector/filter 40 detects the first residual λ₁signal, passes the first residual λ₁ signal and reflects a secondresidual λ₁ signal, the signals λ₂-λ_(n) and the signal λ_(n+1). Filter40 passes the first residual λ₁ signal and reflects a second residual λ₁signal, the signals λ₂-λ_(n) and the signal λ_(n+1). Laser 40 reflectsthe first residual λ₁ signal, the signals λ₂-λ_(n) the signal λ_(n+1)and adds back the signal λ₁ or adds a new signal λ_(n+2).

In the embodiment illustrated in FIG. 8, a laser 25 is coupled to secondoptical transmission path 22. Laser 25 reflects the signals λ₁-λ_(n) andadds a signal λ_(n+1). An optoelectronic device 34 is coupled to fourthoptical transmission path 30. Optoelectronic device 34 can be a filter,detector/filter or laser and multiplexer 12 is an add-drop multiplexeror an optical add.

In FIG. 8, when optoelectronic device 34 is a detector/filter 34,detector/filter 34 passes the first residual λ₁ signal and reflects thesecond residual λ₁ signal, the signals λ₂-λ_(n) and the signal λ_(n+1)which are again received at optical circulator 12. Laser 34 reflects thesignal λ₁-λ_(n), the signal λ_(n+1) and adds the λ_(n+1) signal, all ofwhich are directed to optical circulator 12.

In FIG. 9, multiplexer 10 of FIG. 6 further includes secondoptoelectronic device 40 coupled to fifth optical transmission path 36.Second optoelectronic device 40 can be a detector/filter, filter orlaser. When second optoelectronic device is a laser, Laser 40 reflectssignals λ₁-λ_(n), signal λ_(n+1), and signal λ_(n+2) and adds a signalλ_(n+3). Third optical transmission path 26 transmits signals λ₁-λ_(n),signal λ_(n+1), the λ_(n+2) signal and signal λ_(n+3).

Multiple optical circulators are also used with the present invention.As illustrated in FIG. 10, multiplexer 10 includes optical circulator 12with at least first, second and third circulator ports 14, 16 and 18,and an optical fiber, carrying signals λ₁-λ_(n), with a first opticaltransmission path 20 coupled to first circulator port 14. Second opticaltransmission path 22 is in optical communication with second circulatorport 16. An optoelectronic device 48 is in optical communication withsecond optical transmission path. A second optical circulator 50 has atleast a first, second and third circulator ports 52, 54 and 56respectively. Third optical transmission path 26 is in opticalcommunication with third circulator port 18 and first circulator port52. A fourth optical transmission path 60 is in optical communicationwith second circulator port 54. A second optoelectronic device 62 is inoptical communication with fourth optical transmission path 60. A fifthoptical transmission path 64 is in optical communication with thirdcirculator port 56. Optoelectronic devices 48 and 62 can be adetector/filter, filter, laser amplifier or attenuator.

In one embodiment, multiplexer 10 is an add-add multiplexer whereoptoelectronic devices 48 and 62 are lasers 48 and 62. Laser 48 adds thesignal λ_(n+1). Laser 62 adds the signal λ_(n+2). Signals λ₁-λ_(n),signal λ_(n+1) and signal λ_(n+2) are transmitted at fifth opticaltransmission path 64. Signals λ_(n+1) and λ_(n+2) do not have anyparticular pre-defined wavelength separation from λ₁ to λ_(n)+. In thisconfiguration wavelengths of arbitrary relationship to λ₁ to λ_(n) canbe flexibly added.

In another embodiment, multiplexer 10 is an add-add multiplexer whereoptoelectronic devices 48 and 62 are laser 48 and detector/filter 62.Detector/filter 62 detects and passes the signal λ₁ and reflects thesignals λ₂-λ_(n) and signal λ_(n+1). Filter 62 can be substituted forthe detector/filter. Filter 62 passes but does not detect the signal λ₁and reflects the signals λ₂-λ_(n) and signal λ_(n+1).

Multiplexer 10 of FIG. 10 can include any number of differentcombinations of optoelectronic devices to produce a multi-dropmultiplexer with low cross-talk. Suitable combinations include but arenot limited to detector/filter 48 and detector/filter 62,detector/filter 48 and filter 62, filter 48 and detector/filter 62 aswell as filter 48 and filter 62.

Referring now to FIG. 11, a rejection filter 58 can be used with themultiplexer of FIG. 10. Rejection filter 58 is coupled to third opticaltransmission path 26. In this embodiment, multiplexer 10 is an add-dropor a optical drop multiplexer, and optoelectronic device 48 can be adetector/filter or filter, and optoelectronic device 62 can be adetector/filter, filter or laser.

In other embodiments, a de-multiplexer is provided. Referring now toFIG. 12, a de-multiplexer 110 includes an input fiber 112 carryingsignals λ₁-λ_(n). A first substrate 114 has a first mount surface 116. Afirst optoelectronic device 118 is positioned at first mount surface116. First optoelectronic device 118 can be a detector/filter or afilter. A second optoelectronic device 120 is positioned to receive anoutput from first optoelectronic device 118. Second optoelectronicdevice 120 can be a detector/filter, a filter or a mirror.

In FIG. 12, when optoelectronic device 118 is a detector/filter orfilter, detector/filter 118 and filter 118 each pass a portion of signalλ₁, and reflect a first residual λ₁ signal and signals λ₂-λ_(n). Whenoptoelectronic device 120 is a detector/filter or filter,detector/filter 120 and filter 120 each pass the first residual λ₁signal, and reflect second residual λ₁ signal and signals λ₂-λ_(n). Whenoptoelectronic device 112 is a detector/filter or a filter, andoptoelectronic device 120 is a mirror, mirror 120 reflects firstresidual λ₁ signal and signals λ₂-λ_(n) back to detector/filter orfilter 118 which then reflects the second residual λ₁ signal and signalsλ₂-λ_(n) back to input fiber 112.

As illustrated in FIG. 13, de-multiplexer 110 includes input fiber 112,first substrate 114 with surface 116, a second substrate 122 withsurface 124, optoelectronic device 118 positioned at mount surface 116and optoelectronic device 120 positioned at surface 124. Multiplexer 110of FIG. 13 can include a third optoelectronic device 126 positioned toreceive an output from optoelectronic device 120. Optoelectronic device126 is also a detector/filter or a filter.

Detector/filters 48, 62, 110, 118 and 126 detect a signal, pass aportion of that signal, create and transmit a residual signal andreflect all other signals. Filters 48, 62, 110, 118 and 126 pass aportion of a signal, create and transmit a residual signal and reflectall other signals.

As illustrated in FIG. 14, surface 124 can be reflective. A suitablereflective surface 114 can be made by any flat band highly reflectivemirror. In one embodiment, reflective surface is a silver glassstructure with a level of reflectively that is preferably 95% orgreater. Optoelectronic devices 118 and 120 are both positioned atsurface 114. The output from optoelectronic device 118 is incident onreflective surface 114 which is then reflected to be incident onoptoelectronic device 120. Optoelectronic device 126 can also includedand positioned to receive the output from optoelectronic device 120 thatis reflected from reflective surface 124. Preferably, optoelectronicdevices 118, 120 and 124 are detector/filters or filters.

Another embodiment of a multiplexer 210 is illustrated in FIG. 15.Included are an optical circulator 212 with at least first, second, andthird circulator ports 214, 216 and 218 and a first optical transmissionpath 220 in optical communication with first circulator port 214. Alaser 222 produces signal λ₁ that is transmitted from first opticaltransmission path 220 to optical circulator 212. A second opticaltransmission path 224 is in optical communication with second circulatorport 216. A laser 226 is coupled to second optical transmission path224. Laser 226 is reflective of signal λ₁. Laser 226 need not bereflective if an optional reflective filter 228 is included. Laser 226adds signal λ₂. Signals λ₁ and λ₂ are transmitted to optical circulator;212.

A third optical transmission path is in optical communication with thirdcirculator port 218 and transmits signals λ₁ and λ₂. Optionally, opticalcirculator 212 can receive wavelength division multiplexed opticalsignal including signals λ₃-λ_(n), from an optical input fiber 232. Thesignals λ₃-λ_(n) are reflected by lasers 222 and 226, or filter 216 canbe positioned along each optical transmission path 220 and 224, andoptical circulator 212 transmits signals λ₁, λ₂ and λ₃-λ_(n), as well asany signals received by the multiplexers and de-multiplexers of FIGS.2-14. Multiplexer 210 can be coupled directly or indirectly to any ofthe multiplexers of FIGS. 2-14 and can be used as the multiplexer ofFIG. 1.

Another embodiment of a de-multiplexer 310 is illustrated in FIG. 16. Anoptical circulator 312 includes at least a first, second, and thirdcirculator ports 314, 316 and 318, respectively. An optical fiber with afirst optical transmission path 320 is coupled to first circulator port314 carries a wavelength division multiplexed optical signal includingsignals λ₁-λ_(n), or any of the signals transmitted from themultiplexers and de-multiplexers of FIGS. 2-14. A second opticaltransmission path 322 is in optical communication with second circulatorport 316. An optoelectronic device 324 is in optical communication withsecond optical transmission path 322. Preferably, optoelectronic device324 is a detector/filter or a filter. A third optical transmission pathis in optical communication with third circulator port 318. A secondoptoelectronic device is in optical communication with third opticaltransmission path 326. Preferably, optoelectronic devices 324 and 328are detector/filters or filters. Detector/filters 324 and 328 detect asignal, pass a portion of that signal, create and transmit a residualsignal and reflect all other signals. Filters 324 and 328 pass a portionof a signal, create and transmit a residual signal and reflect all othersignals. De-multiplexer 310 can be coupled directly or indirectly to anyof the multiplexers and de-multipexers of FIGS. 2-14 and can be used asthe DWDM sub-system of FIG. 1.

Each of the detector/filters, filters, lasers and bi-lateral amplifiersof FIGS. 1-16 can be tunable, and in one embodiment be programmablytunable. Additionally, the optical fibers used with the DWDM assemblies,sub-assemblies and devices of the present invention can be metrowavefibers (MWF) disclosed in U.S. Pat. No. 5,905,838, incorporated hereinby reference. An illustrative specification table for a suitablemetrowave fiber is presented:

MWF Specification Table

Attenuation at 1550 nm

<=0.25 dB/km

Attenuation at 1310 nm

<=0.50 dB/km

Effective area at 1550 nm

>=42 microns

Core eccentricity

Less than or equal to 0.8 mu m

Cladding diameter

125+−2.0 microns

Cut-off wavelength

<1250 nm

Zero-dispersion wavelength

1350 nm-1450 nm

Dispersion at 1310 nm

−3.0 to −8 ps/nm-km

Dispersion at 1550 nm

+3.0 to +8 ps/nm-km

Dispersion slope at 1550 nm

0.01-0.05 ps/nm sup 2-km

Macrobendingloss at 1310 nm

<0.5 dB (1 turn, 32 mm)

Macrobending loss at 1550 nm

<0.05 dB (100 turns, 75 mm)

Coating diameter 245+−10 microns

Proof test 100 kpsi

Reel lengths 2.2, 4.4, 6.4, 8.8, 10.8, 12.6, 19.2 km.

EXAMPLE 1

A DWDM sub-system of the present invention is an eight-port opticalcirculator includes six detector/filters and is initially configuredwith three drop channels of two detector/filters each. It is laterreconfigured programmably to include two drop channels each with threedetector/filters. With the reconfiguration there is a reduction incross-talk.

EXAMPLE 2

An adder includes an optical circulator coupled to first and secondlasers. The first and second laser initially produce output signals λ₁and λ₂. The two lasers are then reconfigured programmably to producesignals λ₃ and λ₄.

EXAMPLE 3

A DWDM multiplexer includes an optical circulator coupled to ninelasers. The ninth laser is a backup and can be substituted for one ofthe first eight lasers when one is down. The wavelength relationshipsare flexible relative to the ports and can altered at any time.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formsdisclosed. Obviously, many modifications and variations will be apparentto practitioners skilled in this art. It is intended that the scope ofthe invention be defined by the following claims and their equivalents.

What is claimed is:
 1. A multiplexer for a wavelength divisionmultiplexed optical communication system, comprising: an opticalcirculator including at least a first, second, third and fourthcirculator ports; an optical fiber with a first optical transmissionpath coupled to the first circulator port of the optical circulator andcarrying a wavelength division multiplexed optical signal includingsignals λ₁-λ_(n) and at least one signal λ₁ to be dropped by themultiplexer; a second optical transmission path in optical communicationwith the second circulator port; a first detector/filter coupled to thesecond optical transmission path, the first detector/filter detectingthe λ₁ signal and passing a portion of the λ₁ signal, and reflecting afirst residual λ₁ signal and signals λ₂-λ_(n) to the optical circulator;a third optical transmission path in optical communication with thethird circulator port and transmitting the signals λ₂-λ_(n) receivedfrom the optical circulator; a fourth optical transmission path inoptical communication with the fourth optical circulator port, thefourth optical transmission path being positioned after the secondoptical transmission path and before the third optical transmissionpath; and a first optoelectronic device coupled to the fourth opticaltransmission path.
 2. The multiplexer of claim 1, wherein the firstoptoelectronic device is selected from a detector/filter, a filter and alaser.
 3. The multiplexer of claim 1, wherein the first optoelectronicdevice is a second detector/filter that detects the first residual λ₁signal, passes the first residual λ₁ signal and reflects a secondresidual λ₁ signal and the signals λ₂-λ_(n).
 4. The multiplexer of claim1, wherein the first optoelectronic device is a first filter that passesthe first residual λ₁ signal and reflects a second residual λ₁ signaland the signals λ₂-λ_(n).
 5. The multiplexer of claim 1, wherein thefirst optoelectronic device is a first laser that reflects the firstresidual λ₁ signal and the signals λ₂-λ_(n) and adds back the λ₁ signal.6. The multiplexer of claim 1, wherein the first optoelectronic deviceis a first laser that reflects the first residual λ₁ signal and thesignals λ₂-λ_(n) and adds a λ_(n+1) signal.
 7. The multiplexer of claim3, further comprising: a fifth optical transmission path in opticalcommunication with a fifth optical circulator port, the fifth opticaltransmission path being positioned after the fourth optical transmissionpath and before the third optical transmission path; and a secondoptoelectronic device coupled to the fifth optical transmission path. 8.The multiplexer of claim 7, wherein the second optoelectronic device isa third detector/filter that detects the second residual λ₁ signal,passes the second residual λ₁ signal and reflects a third residual λ₁signal and the signals λ₂-λ_(n).
 9. The multiplexer of claim 7, whereinthe second optoelectronic device is a first filter that passes thesecond residual λ₁ signal and reflects a third residual λ₁ signal andthe signals λ₂-λ_(n).
 10. The multiplexer of claim 7, wherein the secondoptoelectronic device is a first laser that reflects the second residualλ₁ signal and the signals λ₂-λ_(n) and adds back the λ₁ signal.
 11. Themultiplexer of claim 7, wherein the second optoelectronic device is afirst laser that reflects the second residual λ₁ signal and the signalsλ₂-λ_(n) and adds λ_(n+1) signal.
 12. The multiplexer of claim 4,further comprising: a fifth optical transmission path in opticalcommunication with a fifth optical circulator port, the fifth opticaltransmission path being positioned after the fourth optical transmissionpath and before the third optical transmission path; and a secondoptoelectronic device coupled to the fifth optical transmission path.13. The multiplexer of claim 12, wherein the second optoelectronicdevice is a second detector/filter that detects the second residual λ₁signal, passes the second residual λ₁ signal and reflects a thirdresidual λ₁ signal and the signals λ₂-λ_(n).
 14. The multiplexer ofclaim 12, wherein the second optoelectronic device is a second filterthat passes the second residual λ₁ signal and reflects a third residualλ₁ signal and the signals λ₂-λ_(n).
 15. The multiplexer of claim 12,wherein the second optoelectronic device is a first laser that reflectsthe second residual λ₁ signal and the signals λ₂-λ_(n) and adds back theλ₁ signal.
 16. The multiplexer of claim 12, wherein the secondoptoelectronic device is a first laser that reflects the second residualλ₁ signal and the signals λ₂-λ_(n) and adds a signal λ_(n+1).
 17. Themultiplexer of claim 6, further comprising: a fifth optical transmissionpath in optical communication with a fifth optical circulator port, thefifth optical transmission path being positioned after the fourthoptical transmission path and before the third optical transmissionpath; and a second optoelectronic device coupled to the fifth opticaltransmission path.
 18. The multiplexer of claim 17, wherein the secondoptoelectronic device is a second detector/filter that detects the firstresidual λ₁ signal, passes the first residual λ₁ signal and reflects asecond residual λ₁ signal, the signals λ₂-λ_(n) and the signal λ_(n+1).19. The multiplexer of claim 17, wherein the second optoelectronicdevice is a first filter that passes the first residual λ₁ signal andreflects a second residual λ₁ signal, the signals λ₂-λ_(n) and thesignal λ_(n+1).
 20. The multiplexer of claim 17, wherein the secondoptoelectronic device is a second laser that reflects the first residualλ₁ signal, the signals λ₂-λ_(n), the signal λ_(n+1) and adds a signalλ_(n+2).
 21. The multiplexer of claim 8, further comprising: a sixthoptical transmission path in optical communication with a sixth opticalcirculator port, the sixth optical transmission path being positionedafter the fifth optical transmission path and before the third opticaltransmission path; and a first laser coupled to the sixth opticaltransmission path, wherein the first laser reflects the third residualλ₁ signal, the signals λ₂-λ_(n) and adds back the signal λ₁.
 22. Themultiplexer of claim 8, further comprising: a sixth optical transmissionpath in optical communication with a sixth optical circulator port, thesixth optical transmission path being positioned after the fifth opticaltransmission path and before the third optical transmission path; and afirst laser coupled to the sixth optical transmission path, wherein thefirst laser reflects the third residual λ₁ signal, the signals λ₂-λ_(n)and adds a signal λ_(n+1).
 23. The multiplexer of claim 14, furthercomprising: a sixth optical transmission path in optical communicationwith a sixth optical circulator port, the sixth optical transmissionpath being positioned after the fifth optical transmission path andbefore the third optical transmission path; and a first laser coupled tothe sixth optical transmission path, wherein the first laser reflectsthe third residual λ₁ signal, the signals λ₂-λ_(n) and adds back thesignal λ₁.
 24. The multiplexer of claim 14, further comprising: a sixthoptical transmission path in optical communication with a sixth opticalcirculator port, the sixth optical transmission path being positionedafter the fifth optical transmission path and before the third opticaltransmission path; and a first laser coupled to the sixth opticaltransmission path, wherein the first laser reflects the third residualλ₁ signal, the signals λ₂-λ_(n) and adds back a signal λ₁₊₁.
 25. Themultiplexer of claim 2, wherein the detector/filter, filter, and laserare each tunable.
 26. The multiplexer of claim 25, wherein thedetector/filter, filter, and laser are each programmably tunable. 27.The multiplexer of claim 1, further comprising: a bi-directional opticalamplifier coupled to the second optical transmission path positionedbetween first detector/filter and the optical circulator.
 28. Themultiplexer of claim 1, wherein the first detector/filter is an integraldetector and filter device.
 29. The multiplexer of claim 1, wherein thefirst detector/filter includes a non-integral detector and a filter. 30.The multiplexer of claim 1, wherein the λ₁ signal is any wavelength ofthe signals λ₁-λ_(n).
 31. A multiplexer for a wavelength divisionmultiplexed optical communication system, comprising: an opticalcirculator including at least a first, second, third and fourthcirculator ports; an optical fiber with a first optical transmissionpath coupled to the first circulator port of the optical circulator andcarrying a wavelength division multiplexed optical signal includingsignals λ₁-λ_(n) and at least one signal λ₁ to be dropped by themultiplexer; a second optical transmission path in optical communicationwith the second circulator port; a first filter coupled to the secondoptical transmission path, the first filter passing a portion of the λ₁signal, and reflecting a first residual λ₁ signal and the signalsλ₂-λ_(n) to the optical circulator; a third optical transmission path inoptical communication with the third circulator port and transmittingthe signals λ₂-λ_(n) received from the optical circulator; a fourthoptical transmission path in optical communication with the fourthoptical circulator port, the fourth optical transmission path beingpositioned after the second optical transmission path and before thethird optical transmission path; and a first optoelectronic devicecoupled to the fourth optical transmission path.
 32. The multiplexer ofclaim 31, wherein the first optoelectronic device is selected from adetector/filter, filter and a laser.
 33. The multiplexer of claim 31,wherein the first optoelectronic device is a second filter that passesthe first residual λ₁ signal and reflects a second residual λ₁ signaland the signals λ₂-λ_(n).
 34. The multiplexer of claim 31, wherein thefirst optoelectronic device is a first detector/filter that detects andpasses the first residual λ₁ signal and reflects a second residual λ₁signal and the signals λ₂-λ_(n).
 35. The multiplexer of claim 31,wherein the first optoelectronic device is a first laser that reflectsthe first residual λ₁ signal and the signals λ₂-λ_(n) and adds back thesignal λ₁.
 36. The multiplexer of claim 31, wherein the firstoptoelectronic device is a first laser that reflects the first residualλ₁ signal and the signals λ₂-λ_(n) and adds a signal λ_(n+1).
 37. Themultiplexer of claim 33, further comprising: a fifth opticaltransmission path in optical communication with a fifth opticalcirculator port, the fifth optical transmission path being positionedafter the fourth optical transmission path and before the third opticaltransmission path; and a second optoelectronic device coupled to thefifth optical transmission path.
 38. The multiplexer of claim 37,wherein the second optoelectronic device is a first detector/filter thatdetects and passes the second residual λ₁ signal, and reflects a thirdresidual λ₁ signal and the signals λ₂-λ_(n).
 39. The multiplexer ofclaim 37, wherein the second optoelectronic device is a third filterthat passes the second residual λ₁ signal, and reflects a third residualλ₁ signal and the signals λ₂-λ_(n).
 40. The multiplexer of claim 37,wherein the second optoelectronic device is a first laser that reflectsthe second residual λ₁ signal and the signals λ₂-λ_(n), and adds backthe signal λ₁.
 41. The multiplexer of claim 37, wherein the secondoptoelectronic device is a first laser that reflects the second residualλ₁ signal and the signals λ₂-λ_(n), and adds a signal λ_(n+1).
 42. Themultiplexer of claim 34, further comprising: a fifth opticaltransmission path in optical communication with a fifth opticalcirculator port, the fifth optical transmission path being positionedafter the fourth optical transmission path and before the third opticaltransmission path; and a second optoelectronic device coupled to thefifth optical transmission path.
 43. The multiplexer of claim 42,wherein the second optoelectronic device is a second detector/filterthat detects and passes the second residual λ₁ signal, and reflects athird residual λ₁ signal and the signals λ₂-λ_(n).
 44. The multiplexerof claim 42, wherein the second optoelectronic device is a second filterthat passes the second residual λ₁ signal, and reflects a third residualλ₁ signal and the signals λ₂-λ_(n).
 45. The multiplexer of claim 42,wherein the second optoelectronic device is a first laser that reflectsthe second residual λ₁ signal and the signals λ₂-λ_(n), and adds backthe signal λ₁.
 46. The multiplexer of claim 42, wherein the secondoptoelectronic device is a first laser that reflects the second residualλ₁ signal and the signals λ₂-λ_(n), and adds a signal λ_(n+1).
 47. Themultiplexer of claim 36, further comprising: a fifth opticaltransmission path in optical communication with a fifth opticalcirculator port, the fifth optical transmission path being positionedafter the fourth optical transmission path and before the third opticaltransmission path; and a second optoelectronic device coupled to thefifth optical transmission path.
 48. The multiplexer of claim 47,wherein the second optoelectronic device is a first detector/filter thatdetects and passes the first residual λ₁ signal, and reflects a secondresidual λ₁ signal, the signals λ₂-λ_(n) and the signal λ_(n+1).
 49. Themultiplexer of claim 47, wherein the second optoelectronic device is asecond filter that passes the first residual λ₁ signal, and reflects asecond residual λ₁ signal, the signals λ₂-λ_(n) and the signal λ_(n+1).50. The multiplexer of claim 47, wherein the second optoelectronicdevice is a second laser that reflects the signals λ₂-λ_(n), the signalλ_(n+1) and adds a signal λ_(n+2).
 51. The multiplexer of claim 31,wherein the detector/filter, filter, and laser are each tunable.
 52. Themultiplexer of claims 51, wherein the detector/filter, filter, and laserare each programmably tunable.
 53. The multiplexer of claim 31, furthercomprising: a bi-directional optical amplifier coupled to the secondoptical transmission path positioned between first filter and theoptical circulator.